The present invention relates to an automatic speed controller for use in a vehicle, and more particularly to an automatic speed controller which maintains an actual vehicle speed to a preset vehicle speed.
An automatic speed controller has been employed which maintains an actual vehicle speed at a preset vehicle speed. In such an automatic speed controller, an actuator is employed to control a throttle opening to obtain a prescribed vehicle speed which is determined by the vehicle operator. An actuator of the automatic speed controller is controlled by circuits comprised of transistors, diodes, resistors, a microcomputer and so on. These elements are provided on a substrate and are connected to each other.
When a vacuum type actuator is employed in an automatic speed controller, atmospheric pressure or vacuum pressure are alternatively introduced into the actuator in the prescribed cycles, and the rate of atmospheric pressure introduced to the vacuum pressure is varied according to the value of the difference between a preset vehicle speed and a detected actual vehicle speed, thereby adjusting the pressure within the actuator to control the opening of a throttle valve. When vacuum pressure is introduced into the actuator and the control for changing the rate of the atmospheric pressure being introduced to the vacuum pressure breaks because of trouble in the circuits, automatic speed controller cannot maintain the actual vehicle speed at the preset vehicle speed. The result is that the actual vehicle speed becomes higher than the preset vehicle speed.